A. Field of the Invention
This invention relates to a method and apparatus for a fast heat rise resistor that can be used as a resistive igniter. More particularly, this invention relates to the use of resistive foil and photolithographic production to produce a fast heat rise resistor, the resistor suitable for use as an igniter in autoignition-deployed safety devices.
B. Problems in the Art
There are numerous needs for fast heat rise resistors. One such need relates to the use of a resistor as an igniter used to ignite a pyrotechnic or other explosive material. In these resistive igniter applications, it is desirable that the resistive igniter act quickly for rapid ignition. One such application is in vehicle airbag inflators where it is crucial that an igniter act quickly to ignite a gas-generating pyrotechnic in order to ensure that an air bag is deployed in a timely fashion. As the resistor is driven by current, the heat of the resistor increases to a point where other material such as pyrotechnic material can be ignited. There are numerous other applications of resistive igniters, including in other auto-ignition devices such as seatbelt pretensioners, battery cable disconnects, fuel line shut off devices, roll bars, safety devices, and other applications.
There have been attempts made at a resistive igniter in the prior art. Previous attempts have been made that have used metal wire or film bridges. In metal wire or bridgewire devices, a metal filament also known as a bridgewire is used. Some problems with bridgewire devices involve the difficulties involved in manufacturing bridgewires. In order to predict performance of a bridgewire, there must be uniform thermal and electrical properties. Problems remain in manufacturing bridgewires of the needed uniformity.
Another problem with bridgewire devices is that the response time is too slow or else too much activation energy is required. This is problematic where a fast response time is needed or else there are limited power resources that can not support large activation energies. One example of a situation where there are limited power resources is in a vehicle where a 12 volt battery is used to activate an igniter.
Yet another problem with bridgewire devices involves reliability. In bridgewire devices pyrotechnic powder is pressed against the bridgewire. This process can result in detachment of the bridgewire. Thus there are reliability problems with bridgewires as well.
Other attempts at creating resistive igniters have used metal film bridges that are either thin film or thick film. One problem with a thick film or thin film approach is the increased cost of manufacturing associated with these approaches, and in particular with the thin film approach. Another problem with a metal film approach is that there is contact between the metal film bridge and a substrate. This contact between the metal film bridge and the substrate results in a loss of heat from the metal film bridge to the substrate, resulting in an increase in the amount of time for the metal film bridge to reach a particular temperature or alternatively, an increase in the amount of current required in order for the metal film bridge to reach a particular temperature in a given time.
Another problem with film bridges relates to their reliability. Pyrotechnic powder is pressed against the bridge, however, this powder may become displaced during handling. Thus, the pressed powder may or may not constantly touch the wire or film. Where a liquid pyrotechnic is used, the same contact problems may also arise, as the liquid pyrotechnic may not be in constant contact with the wire or film. These problems result in an igniter that is not reliable.
Thus there is a need for a reliable heat rise resistor which has fast response and can be manufactured in a uniform fashion. There is a further need for a heat rise resistor that can be easily packaged and delivered to customers.
Thus, it is a primary object of the present invention to provide an igniter which improves upon the state of the art.
Yet another object of the present invention is to provide an igniter with a fast response time.
Another object of the invention is to provide an igniter that is reliable.
It is another object of the present invention to provide an igniter that requires decreased activation energy.
Yet another object of the present invention is to provide an igniter that can be manufactured uniformly.
Another object of the present invention is to provide an igniter suitable for use in auto-ignition safety devices.
A still further object of the present invention is to provide an igniter suitable for use in an airbag deployment system.
Yet another object of the present invention is to provide a fast heat rise resistor that does not lose heat to a substrate.
It is another object of the present invention to provide a fast heat rise resistor and method of making a fast heat rise resistor that can be easily packaged and distributed.
A still further object of the present invention is to provide a resistor capable of having all of its sides in contact with a pyrotechnic.
These and other objectives, features, or advantages of the present invention will become apparent from the specification and claims.
This invention describes a method and apparatus for a fast heat rise resistor using resistive foil with photolithographic production. The invention provides for a fast heat rise resistor that results in a fast response and is suitable for use as an igniter to ignite pyrotechnic material.